1. Field of the Invention
The invention relates to chemical compounds having n-delocalized electrons, including chromophores, conjugated oligomers, and conjugated polymers.
2. Background
Organic π-conjugated oligomeric or polymeric materials are frequently utilized as organic semi-conductors as they combine solution processing and good charge transport properties with the ability of their electronic structure to be fine tuned to efficiently absorb and emit photons across the solar spectrum. As a result, such materials are used as the active component in several types of electronic and optoelectronic devices, including organic field effect transistors (OFET's), organic light emitting diodes (OLED's), and organic photovoltaic devices (OPV's).
In the area of solar energy conversion, some bulk heterojunction “plastic” solar cells are fabricated with conjugated polymers having backbones comprising alternating donor/acceptor (D/A) comonomer units. This structural motif leads to excited states with charge transfer characteristics and to energy transitions on the order of 1.4 eV. (Refs: 1-10).
Organic materials with very narrow bandgaps (<1.4 eV) that absorb well into the near infrared (NIR) region of the solar spectrum have begun to attract interest as they have potential to be incorporated into NIR photodetectors, NIR photovoltaic and electrochromic devices. The most common method to extend absorption into the NIR region has simply involved increasing the electron acceptor or donor character of D-A type materials to lower the LUMO energy or raise the HOMO energy, respectively. While this strategy has worked to yield many novel NIR absorbing materials, the synthesis has often been multi-step and costly and thus new methods to alter the bandgap of organic materials are desired.